How to create one

Here is a list of useful models:
vacum_entrance_a.mdl
vacum_flange_a.mdl
vactube_connector.mdl
Making items inside
First, start by making path_tracks. Don't forget to turn on 'Teleport to this path' in the first 'path_track'.

Now create 2 prop_dynamic_overrides, and 3 brushes in the same place. Convert two of them to func_rotating and the 3rd one to func_tracktrain.
Parent prop_dynamic to func_rotatating, func_rotating to 2nd func_rotating, and then to func_tracktrain. Set track train speed to 450-600, height above track to 0 and distance between the wheels to 0. Now go to flags and check allow roll (z-rot). Now open both of func_rotatings and in flags check x axis in the first and y axis in 2nd. Set rotating speed to 150.

Now set 2 different models to prop_dynamics_overrides. Create logic_auto and give it outputs.
Output Name Activator Via this input
On Map Spawn prop_dynamic_override1 turn off
On Map Spawn prop_dynamic_override2 turn off